Introduction

Twenty some years ago, programmable logic controllers revolutionized how industrial machinery was controlled. Devices that are today the size of an operator’s lunch box replaced the big cabinet filled with relays and miles of wire interconnecting them. A similar revolution may be underway today with digital switching systems that are being applied in the marine and transportation industries. These new systems could be a benefit or a nuisance to relay and switch manufacturers.

This article will look at this new technology, how it is put together, its features and benefits, and where it may be deployed next.

Origins of the Technology and Basic Functions

Digital data buss (DDB) technology was developed in the automotive industry to enable communication between various controllers in a vehicle. Two types of architecture exist. The general type of DDB requires complex multi-way data exchange at high rate and frequency. The focused DDB centralizes control and polls input devices for a change in state, then initiate the appropriate output. The focused DDB requires far less processing power making them less expensive to construct.

Manufacturers such as Cole Hersee, Carling Technologies, Digital Switching Systems (a DNA Group subsidiary), and Eaton have developed systems that utilize focused DDB technology to take operator and machine input to control electrical devices in the marine and transportation equipment markets.

These new digital switching systems are capable of far more than basic on/off control. The ability to program functions using logic and time gives these systems enhanced capabilities. They can control functions like intermittent windshield wiper control, require engine compartment blowers to operate for a specific period of time before engine start, control groups of devices simultaneously, sequence the operation of devices, and incorporate H bridges for bi-directional motor control, and more.

System Components

Digital switching systems utilize three component parts: a controller, input devices, and a communications cable.

The controller is the brains and brawn of the system. It can control 20 or more electrical circuits carrying resistive, reactive, or inductive loads up to 20 amperes. The controller also contains the processing power to communicate with input devices and perform the appropriate programmed functions. Circuit protection is an additional function of the controller. In the case of electromechanical controllers, traditional relays provide control in-line with circuit breakers. Solid-state controllers use MOSFETs for control and circuit protection. Solid-state controllers can be programmed to trip circuits if a programmed threshold current is reached. These controllers are then connected to input devices.

Input devices are typically a keypad or discrete switch. Keypads are usually dome arrays, with backlighting, function indicator, and a micro controller. The function indicators announce two things — a constant glow of the indicator can show the proper function of a device while a flashing indicator can signal a fault condition. Standard keypads are offered and custom keypads that offer unique styling can be made. The systems are capable of controlling a function from multiple keypads at different locations.

Discrete switches can also be incorporated. These can be rockers, toggles, push buttons, snap action or others. An interface board with a micro controller is required for connection and communication of these switches with the controller.

The last piece is the communications cable that ties the system components together. These four wire cables use a twisted pair for communication. Two wires each carry bi-directional transmit and receive codes. The bi-directional communications enables a much larger difference between high and low voltage states reducing the potential effect of induced noise. The other two wires carry power for indicators and other components.

Features and Benefits

Digital switching systems have many appealing features and benefits that are driving their popularity in the marine and transportation industries.

Keypad design flexibility and foot print reduction — since the switching of high amperage or voltage loads is taking place remotely a bank of large switches capable of switching these loads can be replaced by a much smaller keypad. Designers also have greater freedom in the creation of keypad that enhance and differentiates the appearance of their product.

The combination of circuit control and protection into a single device simplifies and cost reduces.

Reduced Wiring Cost and Reliability

Controllers can be strategically located near the devices they manage. This can reduce the cost of wiring by an estimated 60%. A shorter run of wire on high amperage loads reduces line loss and saves energy. Estimates show the number of connectors can be reduced 50% when using a digital switching system. This, of course, saves the cost of the connectors and improves on system reliability since connection points can be faulty.

System expandability and scalability — multiple controllers can be utilized in a master/slave scheme enabling the addition of more input and controlled devices.

With the most basic systems costing less than $100, the added design flexibility, enhanced aesthetics, system simplification, scalability and expandability with a lower installed cost than traditional methods provides a great combination of features and benefits that is increasing the use of these systems.

Where to next

Current digital switching systems have been designed for application in the transportation and marine environments. Meaning they are constructed for harsh locations and operate on DC loads. In this form they could also be used in agricultural and construction equipment. Perhaps these systems can be modified for applications in other products where multiple electrical devices need to be controlled, such as, appliances and commercial and industrial equipment.

How Will This Effect Switch and Relay Makers

For relay makers the manufacturers of electromechanical controllers should become a potential new customer. For switch producers, the first thought is switch usage will drop as direct switching functions are eliminated. This may be the case. However, some designers and users may prefer the traditional look and feel of a switch versus a keypad. So there may be an opportunity to develop push button, rocker, rotary, and toggle switches to apply in digital switching. Also, some the electromechanical controllers are equipped with by-pass switches that permit loads to be controlled independently so each circuit still has a switch. All these new digital switching systems may be more of an opportunity than threat for relay and switch sales.